1. Technical Field
The present invention relates to a signal transmission circuit, a data transfer control and an electronic device.
2. Related Art
In the universal serial bus (USB) 2.0, a transmission mode called a high speed (HS) mode is prepared in addition to a full speed (FS) mode defined in the old USB 1.1. In the HS mode, data is transmitted with 480 Mbps, realizing high speed data transmission, compared to the FS mode, in which data are transmitted with 12 Mbps.
The signal transmission circuit for the HS mode includes a constant current circuit for generating a high-level voltage (400 mV) for transmission and operates differential signal lines DP (Data+) and DM (Data−) of USB by using a constant current (17.8 mA) generated by the constant current circuit.
In the HS mode, however, the transmission rate is high, like a theoretical value of 480 Mbps. Further, products that clearly do not observe a standard such as the eye pattern of USB exist in the market. Hence, in the case when data transmission control devices at a receiving side do not observe the USB standard, data may not be normally transmitted even when a transmission side observes the USB standard.
JPA 2002-344864 is an example of related arts.